The former double agent Sergei Skripal and his daughter, Yulia, could have been exposed to a deadly nerve agent through his car’s ventilation system, US media have reported.

The pair remain critically ill in hospital after being exposed to the nerve agent novichok in Salisbury, in the UK, two weeks ago.

The US organisation ABC News reported that intelligence officials had said the nature of the substance used, described as “dusty”, was now clear and that UK officials had a better picture of how the attack was carried out, saying that the Skripals could have been exposed to the substance through the BMW’s ventilation system.

The development comes as counter-terrorism police renewed their appeal for sightings of Skripal’s burgundy BMW 320D saloon car, registration HD09 WAO, in Salisbury on the morning of 4 March.

Neil Basu, a Metropolitan police assistant commissioner, said: “We are learning more about Sergei and Yulia’s movements but we need to be clearer around their exact movements on the morning of the incident.” Scotland Yard would not comment on the ABC News report.

ABC also reported that intelligence officials had said that up to 38 individuals in Salisbury had been identified as having been affected by the nerve agent, but that the full impact was still being assessed and more victims were expected to be identified.

This is not the first time the US media have reported updates from intelligence officials about incidents in the UK. British police temporarily suspended intelligence sharing with the US after the Manchester Arena bombing in May 2017 following a series of leaks to American media.

The US television network CBS disclosed the name of the Manchester suicide bomber, Salman Abedi, citing American sources, at a time when the British authorities were asking media to withhold information to protect the investigation. Additionally, the New York Times published detailed photographs taken at the bomb scene that had been taken by British investigators.

Meanwhile, the Sun on Sunday reported that Yulia Skripal’s boyfriend was a Russian secret service agent. The newspaper also said she had worked in the US embassy in Moscow.